Latent tuberculosis infection: the final frontier of tuberculosis elimination in the USA

Abstract

Since 1989, the USA has been pursuing the goal of tuberculosis elimination. After substantial progress during the past two decades, the rate of tuberculosis cases in the USA each year has now levelled off and remains well above the elimination threshold. Both epidemiological data and modelling underline the necessity of addressing latent tuberculosis infection if further progress is to be made in eliminating the disease. In this Personal View we explore next steps towards elimination. Given the estimated prevalence of latent tuberculosis infection, compared with the limited testing and treatment that currently occur, a major new effort is required. This effort should consist of a surveillance system or registry to monitor progress, scale-up of targeted testing for latent tuberculosis infection in at-risk populations, scale-up of short-course treatment regimens, engagement of affected communities and medical providers who serve those communities, and increased public health staffing for implementation and oversight. Such an effort would benefit greatly from the development of new tools, such as tests that better indicate reactivation risk, and even shorter latent tuberculosis infection treatment regimens than currently exist.

Figure 1. Reported tuberculosis cases in the USA, 1982–2014

Data from US Centers for Disease Control and Prevention.

Figure 2. Trends in tuberculosis cases in foreign-born people in the USA, 1993–2014

Data from US Centers for Disease Control and Prevention.

Figure 3. Latent tuberculosis infection prevention cascade using the example of contact investigation

The cascade consists of multiple steps: identifying the population at risk, testing the population at risk for latent tuberculosis infection, and evaluating those with positive tests to exclude tuberculosis; initiating treatment in those with latent tuberculosis infection, and completing treatment for those who start. People can fail to complete any of the steps, and the effect is multiplicative. In this example, it is assumed that 93% of contacts have been identified and 82% of those have a complete evaluation. Of the contacts with latent tuberculosis infection (21%), 71% start treatment, and 46% of those who start treatment complete it. Thus, only 33% of contacts with latent tuberculosis infection complete treatment.